Nil、nil、NULL、 [NSNULL null]、@""的异同

NSString*str1 =nil;

NSString*str2 =Nil;

NSString*str3 =NULL;

NSNull*str4 = [NSNullnull];

NSString *str5 = @"";

NSLog(@" \r str1:%p\r str2:%p\r str3:%p\r str4:%p\r str5:%p\r", nil, NULL, Nil, [NSNullnull], @"");
NSLog(@"\r str1:%@\r str2:%@\r str3:%@\r str4:%@\r str5:%@\r", str1, str2, str3, str4, str5);

结果：
2013-05-09 16:42:00.124 Targets[674:c07]
str1:0x0
str2:0x0
str3:0x0
str4:0x1dc2678
str5:0x46f4

2013-05-09 16:42:04.717 Targets[674:c07]
str1:(null)
str2:(null)
str3:(null)
str4:
str5:

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2.描述
Printing description of str1:

Printing description of str2:

Printing description of str3:

Printing description of str4:

Printing description of str5: